1. Field of the Invention
This invention is in the field of image analysis and more particularly is a system for providing a display representative of selected objects of a scene.
2. Description of the Prior Art
To provide a video signal representative of a scene, typically a video source, such as a television camera, has an optical input which receives light flux along a line of sight from a point on the scene. The amount of the light flux is a non-linear function of what is known in the art as an image photo-density of the point. The video signal has an amplitude which is proportional to the amount of the light flux.
Usually, the line of sight successively traces an array of closely, evenly spaced lines across the scene. The lines are traced from left to right at a constant rate.
The array of lines is referred to in the art as a camera raster and each of the lines thereof is referred to as a camera raster line. Typically, a first camera raster line is traced across the topmost portion of the scene and a last camera raster line is traced across the bottom of the scene. After the first camera raster line is traced, the line of sight is rapidly retraced during a horizontal retrace time from right to left to a position slightly below the first camera raster line to trace the next succeeding camera raster line. Other camera raster lines are traced in a similar manner. After the last camera raster line is traced, the line of sight is rapidly retraced during a vertical retrace time to a position to trace the first camera raster line.
Because the camera raster lines are traced at a constant rate, a camera raster line traced on large objects (of substantially uniform image density) of the scene cause infrequent variations in the amplitude of the video signal. Correspondingly, a camera raster line traced on small objects of the scene causes frequent variations in the amplitude of the video signal. Therefore, the video signal has a frequency spectrum of components respectively associated with the sizes of the objects of the scene.
Heretofore, large computers or other large costly apparatus has been used for providing a display representative of sizes and image densities of objects of a scene. A large computer is typically programmed to process representations of predetermined video signals. Accordingly, the large computer is not suitable for providing an on-line (real time) display representative of the sizes and the image densities of the objects.